1. Field of the Invention
The invention relates to a crankshaft for a reciprocating internal combustion engine, comprising a crankpin and an eccentric sleeve, which is rotatably mounted on the crankpin by means of a cylindrical inner surface, the sleeve having at least one locking recess, in which a locking element can engage in order to cancel the rotatability of the sleeve about the crankpin.
2. Disclosure Information
A crankshaft of the type described is generally known from DE 197 03 948 C1. A crankshaft of this kind is used to change the compression ratio of a reciprocating internal combustion engine by shortening or lengthening the effective length of the connecting rod as described below.
The connecting rod is attached by its first end in a known, articulated manner to the piston, which moves up and down in the cylinder of the engine, and the connecting rod is arranged in an articulated manner by its second end on the crankpin of the crankshaft. The connecting rod converts the linear upward and downward movement of the piston into a continuous rotary motion of the crankshaft. According to DE 197 03 948 C1, the connecting rod is mounted on the crankpin by its second end by means of an interposed eccentric sleeve. The eccentric sleeve has a cylindrical inner surface and a cylindrical outer surface, which is eccentric relative to the latter. The effective stroke length which can be defined, together with the connecting rod, as the distance between the axis of rotation of the connecting rod on the piston and the axis of rotation of the crankshaft, differs depending on the rotation of this eccentric sleeve relative to the crankpin. By rotating the eccentric sleeve, it is thus possible to modify the compression that occurs in the swept volume of the engine""s piston and hence the behavior of the engine.
In order to be able to perform this modification of the compression in a selective manner, the sleeve disclosed in DE 197 03 948 C1 has a recess on each of its two axial edges, the two recesses lying diametrically opposite relative to the center of the sleeve. Arranged at the end of the connecting rod there is furthermore a locking element, which can be displaced between two positions parallel to the axis of the sleeve. In the first position, this locking element engages with a locking effect in the first recess of the sleeve, while in the second position it engages with a locking effect in the second recess. Since the two recesses lie diametrically opposite one another on the sleeve, the sleeve must rotate through 180xc2x0 about the crankpin to achieve a change between the two positions of engagement of the locking element. At the same time, the recesses in the sleeve are arranged in such a way in relation to the eccentricity of the sleeve that the maximum and minimum possible effective length of the connecting rod is obtained in the engaged positions of the locking element.
According to DE 197 03 948 C1, a movable mechanism that is independent of the connecting rod is provided at the end of the connecting rod for the purpose of actuating the locking element, being arranged by means of an arcuate stop surface on the edge of the space for the motion of the connecting rod. The extent of the stop surface must be large since the end of the connecting rod moves during the operating of the engine and it must be possible to switch over the locking element in every possible position. Accordingly, DE 197 03 948 C1 results in a relatively complex, expensive and fault-prone mechanism for actuating the locking element and modifying the effective length of the connecting rod.
Faced with this situation, it is the intention of the present invention to improve a crankshaft of the type stated at the outset in such a way that it can be produced at lower cost, with robust, reliable operation.
According to the present invention, a crankshaft for a reciprocating internal combustion engine comprises a crankpin that is arranged eccentrically with respect to the axis of rotation of the crankshaft. The crankshaft furthermore comprises an eccentric sleeve, which is rotatably mounted on the crankpin by means of a cylindrical inner surface and a cylindrical outer surface which is eccentric with respect to the inner surface. One end of a connecting rod can be mounted on the outer surface of the sleeve, it being possible, thanks to the eccentricity of the sleeve, to modify the effective length of the connecting rod together with the stroke radius by rotating the sleeve about the crankpin. The sleeve has at least one locking recess or pocket, in which a locking element can engage in order to cancel the rotatability of the sleeve and thus lock the sleeve on the crankpin. Locking the sleeve has the effect of fixing the current effective length of the connecting rod.
The crankshaft is distinguished by the fact that the at least one locking element is arranged on the crankshaft and that the crankshaft contains control means for the actuation of the locking element. Unlike the prior art, the locking element is thus not arranged in the connecting rod but on or in the crankshaft. This has the advantage that control means for actuating the locking element can likewise be provided on or in the crankshaft, where they are easier to accommodate in terms of manufacturing and where they are protected from disturbing influences. Moreover, there is no need for complex and bulky additional elements in the space below the connecting rod in order to actuate the locking element. The crankshaft according to the invention thus also permits a more compact engine construction.
According to a preferred embodiment of the present invention, control means that are provided in the crankshaft, comprising feed lines for a hydraulic fluid, and the locking elements are hydraulically actuable. The passages for hydraulic fluid in the crankshaft lead to the pressure-actuated locking elements. There is sufficient space for passages of this kind in the crankshaft and the arrangement of the passages is advantageous in terms of manufacturing, not the least because oil passages for lubricating the bearings generally have to be provided in the crankshaft anyway.
The hydraulically actuable locking elements contain a swept volume for the accommodation of hydraulic fluid and a plunger that can be moved by a change in the volume of the swept volume. The locking elements are preferably preloaded mechanically into a position of rest, from which they can be moved when a hydraulic (excess) pressure is applied. The position of rest of the locking element can correspond either to engagement of the locking element in the recess of the sleeve or to retraction of the locking element from the sleeve.
According to another aspect of the invention, the crankshaft has at least one fluid feed passage leading to the outer surface of the crankpin (and hence to the inner surface of the sleeve), and the sleeve is shaped in such a way on its inner surface that feeding in a fluid via the fluid feed passage produces a torque about the crankpin at the sleeve. This means that the rotation of the sleeve about the crankpin required to modify the effective length of the connecting rod can be actively performed or assisted by the selective supply of a fluid via the fluid feed passage. The crankshaft according to the invention is thus not dependent on the rotation of the sleeve after the release of the locking taking place spontaneously on the basis of the forces that are acting; on the contrary, this rotation can be performed actively and in a predetermined direction.
There are various possibilities for the shape of the sleeve on its inner surface that leads to the desired torque when a fluid is supplied. In particular, the sleeve can have an encircling sawtooth shape on its inner surface, the sawteeth extending radially. When a fluid is fed into the asymmetric recesses between the sawteeth, force components of different magnitude are produced in the positive and negative directions of rotation, with the overall result that the desired propulsion in one direction of rotation occurs.
According to a development of the last-mentioned embodiment, the crankshaft has a fluid outlet passage, via which fluid that has been fed to the inner surface of the sleeve via the abovementioned fluid feed passage can be discharged. The fluid is thus fed via the fluid feed passage and the inner surface of the sleeve into the fluid outlet passage in a single stream, and it can preferably be guided in a circuit. On its way between the fluid feed passage and the fluid outlet passage, the fluid enters into interaction with the sleeve and gives rise to the desired torque there.
The crankshaft preferably comprises two locking elements, which are arranged offset by 180xc2x0 on the crankpin. As used herein the term xe2x80x9con the crankpinxe2x80x9d includes a situation where the locking elements are arranged in the crankpin itself or on its edge, i.e. in the so-called webs of the crankshaft, from where they can engage in the locking recess in the sleeve. Preferably, only a single locking recess is provided in the sleeve, thus allowing only one of the locking elements to engage in this recess at any given time. Since the locking elements lie opposite one another at 180xc2x0, they can be used to bring about corresponding locking of two positions of the sleeve that are rotated by 180xc2x0 relative to one another. At the same time, the arrangement of the recess in the sleeve and of the locking elements is preferably chosen in such a way that the maximum possible and minimum possible effective length of the connecting rod respectively are achieved in the locked positions.
To enable the feed lines to the locking elements and, where appropriate, the fluid feed passage to be accommodated efficiently, the crankshaft preferably has an internal hole running along its length, in which separate passages for the abovementioned lines are arranged.